This invention relates to multilayer metal foil and metal sheet structures which have utility as heat shields and as acoustic shields.
Multilayer metal foil insulation has been used for many years, as illustrated by U.S. Pat. No. 1,934,174. Such metal foil insulation has typically been used in high temperature applications for reflective heat insulation. In those applications, the layers of metal foils are embossed to provide separation between the layers, and the stack of layers are protected in a container or rigid cover to prevent the stack of metal foils from becoming compressed at any portion, which would decrease the heat insulation value of the stack.
U.S. Pat. No. 5,011,743, discloses that multilayer metal foil insulation can provide enhanced performance as a heat shield when a portion of the multilayer metal foil is compressed to provide a heat sink area through which heat is collected from the insulating portions of the stack and dissipated from the heat shield. Such multilayer metal foil heat shields are formed from a stack of embossed metal foil layers by compressing portions of the stack to create the desired heat sink areas. The layers are attached to each other or stapled together to prevent the layers from separating. The heat shields and acoustic shields formed according to the disclosure of the U.S. Pat. No. 5,011,743 are typically compressed in the heat sink areas and cut to a desired pattern. Such multilayer metal foil heat shields do not normally have sufficient structural strength for stand-alone use in many applications. For many applications, the metal foil heat shields are typically attached to a structural support member or pan to provide a final assembly which is then placed in service as a heat shield or acoustic shield. The support members are typically metal pans, metal stampings or metal castings. Typical applications for such heat shield assemblies include automotive heat shield applications.
The disclosures of the above patents are incorporated herein by reference.
It is an object of this invention to provide a multilayer metal foil insulation structure which is flexible and suitable for use in heat shield and acoustical shield applications.
The flexible corrugated multilayer metal foil structure according to this invention comprises a stack of metal foil layers which are formed in corrugations extending across a stack of the metal foil layers, wherein all of the layers have the same corrugated pattern and shape as a result of the stack being shaped in corrugations or the layers being separately shaped in corrugations then nested into a stack. A portion of the corrugations of the stack of metal foil layers is compressed to fold the layers together whereby the layers are interlocked together in overlapping relationship. The resulting multilayer corrugated interlocked structure is flexible by means of the ability of the multilayer corrugated interlocked structure to flex along the valleys or peaks of the corrugations where they are not compressed and folded and along the valleys between the corrugations where the peaks of the corrugations are compressed and folded to interlock the layers together. Depending on the thickness of the layers, number of layers and the degree of compression of the interlocked layers, the compressed portions of the corrugations can also flex along with the uncompressed portions of the interlocked structure.
The flexible corrugated multilayer metal foil structures of this invention comprise at least three metal layers at least two of which are metal foil layers having a thickness of 0.006 in. (0.15 mm) or less. It is generally preferred that the flexible corrugated multilayer structures of this invention contain at least three layers of metal foil and more preferably will typically contain five or more layers of metal foil. Preferably, the metal foil layers will be 0.005 in. (0.12 mm) or less, with 0.002 in. (0.05 mm) metal foil being a preferred thickness, especially for the interior layers of the flexible corrugated multilayer metal foil structure. In addition to the layers of metal foil, optional protective exterior layers of metal sheet on one or both sides of the flexible corrugated multilayer structure can be included. Such metal sheets have a thickness greater than 0.006 in. (0.15 mm) and up to about 0.050 in. (1.27 mm). The thickness of the optional exterior protective metal sheet is selected such that it can be corrugated into the same shape and pattern as the other layers (either separately then nested, or simultaneously corrugated as part of the stack) and compressed into interlocking engagement with the other layers as part of the unitary multilayer metal foil structure according to this invention. Preferably, the protective exterior metal sheet layer will be between about 0.008 in. (0.20 mm) and about 0.030 in. (0.76 mm). One preferred flexible corrugated multilayer metal foil structure according to this invention is made entirely of metal foils each having a thickness of 0.006 in. or less without the use of heavier external sheet layers.
One or more of the individual metal foil layers comprising part of the multilayer structure of this invention may be embossed or contain other spacers to provide spaces and gaps between the layers. Even though some of the embossments or gaps may be reduced during the formation of the corrugations of the multilayer stack and some may be entirely eliminated in those areas where the corrugations are compressed to form the folds interlocking the layers together, the residual spaced apart gaps between the layers in various parts of the multilayer corrugated structure is advantageous in many applications with respect to the heat and acoustic insulating and shielding properties. However, without embossments or other spacers to hold the layers apart, the metal foil layers will inherently have some gaps and spaces between the layers due to wrinkles or other deformations that inherently occur during the formation of the corrugations of the multilayer metal foil structure. In addition to spacers in the form of embossments or wrinkles in the layers themselves, separate spacers may be used to provide gaps between the layers, such as compressible foil pieces or mesh, or non-compressible materials, so long as the presence of such spacers does not interfere with the compression and folding of the corrugations together at desired locations in the structure to interlock the layers and prevent separation of the layers when the multilayer metal foil structure is used for its intended use.
The flexible multilayer corrugated metal foil structures of this invention, when formed with corrugations across the stack of layers, are rigid or at least resist bending in one direction but are flexible in the other direction due to the ability of the stack to flex along the peaks and/or valleys of the corrugations. This flexibility of the multilayer corrugated structure enables application thereof as heat and sound shields to contoured shapes, especially curved planar surfaces such as conduits. However, the multilayer corrugated structures of this invention can also be fitted or formed into or onto any shape desired by flexing the multilayer structure in one direction along the corrugations and by bending, creasing or buckling the corrugation ridges to shape the structure in the other direction across the corrugations. In addition, the spacing of the corrugations can be laterally stretched out or compressed together to assist in shaping the multilayer corrugated metal foil structure to fit desired three dimensional shapes. For example, a shield can be formed to a desired shape by forming the corrugations in the stack of metal foil layers, shaping the stack including stretching or compressing the corrugations laterally (along the plane of the layer) as needed for shaping, then compressing the corrugations vertically where desired to fold the corrugations and interlock the layers together.
In an optional structure, the corrugated multilayer metal foil structure of this invention can be made flexible in the other direction by compressing creases across the corrugations, whereby the creases are compressed deeply enough into the corrugations to provide the bending and flexing of the multilayer structure along those creases. It will be recognized that in the formation of such creases to provide additional flexibility to the corrugated multilayer metal foil structure of this invention, the compression to form the creases will also provide the additional function of folding the corrugated layers and interlocking the layers together with one another in the same fashion as the above described vertical compression of the corrugations to interlock and prevent separation of the layers. This folding and interlocking of the layers by the creasing can be in addition to or instead of the first compression of the corrugations mentioned above to fold and interlock the layers. Such creases can be any desired width, from a knife-edge sharp crease to wide flattened strip across the corrugations, and can be any desired direction across the corrugations depending on the flexibility and the heat or sound shielding properties desired in the final product.
The present invention provides a method of forming a flexible corrugated metal foil structure by first providing a stack of metal foils. Each metal foil layer optionally may be individually embossed, wrinkled, corrugated (for example, very small corrugations in period or height compared to the main corrugations of the multilayer product) or contain other spacers to provide gaps between the layers. The stack of metal foils is then shaped as a unitary structure into corrugations, which may be done using conventional metal corrugating methods and equipment. After the corrugations are formed in the multilayer stack, a portion of the corrugations are compressed to fold the layers over each other whereby the layers are interlocked together. The interlocking of the layers prevents separation of the layers while retaining the flexibility of the multilayer metal foil corrugated stack along the corrugations by flexing along the peaks and valleys or channels of the corrugations. The portion of the corrugations which are compressed in order to fold and interlock the layers may be any portion or area of the corrugations desired for a particular product, but sufficient to prevent separation of the layers during handling and use. For example, in many applications it will be preferred that the edges of the corrugated stack be compressed whereby the metal foil layers are folded and interlocked around the perimeter or along at least one edge of the multilayer corrugated metal foil stack. Other configurations may be desirable depending on end use of the multilayer metal foil structure. For example, it may be desired to compress an interior portion of the corrugations in a strip parallel with the edge of the multilayer strip whereby the layers are folded and interlocked together in an interior portion of the corrugated multilayer metal foil structure leaving the edges uncompressed in the corrugated configuration. Alternatively, it may be desired to substantially compress periodic or alternating corrugations along all or most of the length of each individual corrugation, whereby a certain proportion of the corrugations are compressed to fold and interlock the layers together while the entire length of other corrugations remain uncompressed.
The shape of the corrugations can be selected by one skilled in the art depending on the desired properties of the structure. For example, the corrugations may be sinusoidal, square, rectangular, semicircular or other appropriate corrugation shape. The size, height, width and spacing of the corrugations can be uniform and regular, or can be nonuniform and irregular, so long as the corrugations are designed so that when the selected portion of the selected corrugations are compressed, the layers will readily fold and interlock together as a result of the compression of the corrugations. Similarly, the shape of the folds into which the layers are deformed and locked together can be selected and designed depending on the interlocking properties desired in the final flexible corrugated multilayer metal foil product produced according to this invention.
The flexible multilayer metal foil structures of the present invention have a wide range of utilities, but are preferred for heat and acoustical shielding applications, particularly in automotive use. The flexible multilayer metal foil structures of this invention have utility as heat insulating materials, but are preferred for use in heat shielding applications for spreading and dissipating heat from point sources of heat, or hot spots. Due to the high lateral conductivity of the multiple metal layers, heat can be efficiently conducted laterally from a hot spot to other locations within the flexible multilayer metal foil structure where the heat can be absorbed by or dissipated into surrounding environment where the temperature is lower than in the area of the hot spot heat source. It will be expected that in the corrugated multilayer metal structure according to the present invention, heat will be most readily and rapidly conducted along the shortest conductive path, which is along the length of the channels of the corrugations. Heat will be conducted more slowly in the direction transverse to the corrugation channels, i.e., along or across the peaks and valleys of the corrugations. Heat will also be conducted more rapidly along the paths resulting from the compressed areas and the creased areas referred to above, where the peaks and valleys of the corrugations have been essentially flattened. Given these properties, one can readily design corrugated multilayer metal foil heat shielding structures according to the present invention to shield and insulate hot spot sources of heat by conducting and dissipating the heat laterally along the corrugations in desired and specific directions. Similarly, the flexible multilayer metal foil structures of this invention have utility as acoustical shields due to the vibration and sound absorbing properties of the corrugated multilayer metal foil structure. For acoustic applications, it will be apparent to one skilled in the art that it may be desirable to have alternate material layers in between the corrugated metal layers. Materials such as plastic films, adhesives, fibers and other materials may be used to enhance the acoustic damping properties of the multilayer corrugated metal foil structure, although some of those alternate materials may not be suitable for use in some heat insulation or heat shielding applications.
The corrugated multilayer metal foil structure of this invention provides two advantages for utilization of the structure in various heat and acoustic shielding and insulating applications. First, the flexibility provided by the corrugations provides convenience in positioning the flexible corrugated multilayer metal foil structure of this invention in desired applications. As will be recognized, the additional flexibility by providing the above-referenced longitudinal creases across the corrugations provide additional flexibility, or the preforming the corrugated stack of metal foil layers before interlocking the layers together, will enable one to utilize the structures of this invention where various shapes of heat or acoustic shielding are required. The second property provided by the corrugated multilayer metal foil structure of this invention is the surprisingly high vertical strength and load bearing capability of the flexible corrugated multilayer metal foil structure formed according to this invention. After the selected portions of the corrugations are compressed to form the folding and interlocking of the layers together, the remaining uncompressed portions of the corrugations will support vertical loads and exhibit resistance to compression higher than one would expect for metal foils. Such load bearing properties make the flexible corrugated multilayer metal foil structures of this invention particularly useful as heat and acoustic shields under the carpet in passenger compartments of vehicles. The corrugated multilayer metal foil structures according to this invention may be positioned between the floor pan of an automobile and the passenger compartment carpet to absorb and dissipate heat from hot spot sources underneath the floor pan, such as a catalytic converter or exhaust systems, and to absorb and dampen noise, such as road noise. The corrugated shape of the multilayer metal foil structures of this invention provides sufficient resistance to compression and crushing under the carpet to enable the corrugated metal foil structure to maintain its corrugated shape and its heat and acoustic shielding properties under ordinary usage where vertical loads are applied to the corrugated multilayer metal foil structures by passengers stepping on the carpet.
It will be recognized by one skilled in the art that the flexible corrugated multilayer metal structures according to this invention can be formed with metal sheets having thicknesses greater than 0.006 in. and without the use of metal foil layers having a thickness of 0.006 in. or less. Such flexible corrugated multilayer metal sheet structures are formed in the same way as the multilayer metal foil structures and may be desirable for additional strength and vibration resistance in certain end use applications.